This tool calculates a stepper motor’s maximum step rate, RPM, minimum step time, time constant, and peak power, from supply voltage, current, inductance, and steps per revolution.
Find a Stepper Motor’s Maximum Step Rate for a Given Supply Voltage
This tool converts supply voltage, rated current, phase inductance, and steps per revolution into the maximum step rate, rotational speed, timing, and power figures for a stepper motor driven in constant-voltage (L/R) mode. Motor control and firmware engineers use it to set safe maximum feedrates for 3D printers, CNC axes, and open-loop positioning stages before bench-testing a driver and motor pairing.
Entering Voltage, Current, Inductance, and Steps per Revolution
Enter the driver’s supply voltage (V), the motor’s rated phase current $I_{max}$ (A), per-phase inductance $L$ (mH), and steps per revolution. The tool returns maximum step rate, RPM, angular velocity, minimum step time, time constant, peak power, stored energy, and current slew rate.
How Supply Voltage and Winding Inductance Set the Step Rate Limit
Per the stepper motor calculator published by All About Circuits, the minimum time a winding needs to swing from $-I_{max}$ to $+I_{max}$ under a constant applied voltage, and the resulting maximum step rate and speed, are:
$$t_{min} = \frac{2 L I_{max}}{V} \qquad f_{max} = \frac{1}{t_{min}} \qquad \text{Max Speed (rev/s)} = \frac{V}{2 L I_{max} \cdot spr}$$
$$P_{max} = I_{max} \times V$$
The remaining outputs follow from standard Ohm’s law and RL-circuit relationships applied to the same $V$, $I_{max}$, and $L$: implied resistance $R = V/I_{max}$, time constant $\tau = L/R$, stored magnetic energy $E = \tfrac{1}{2}LI_{max}^2$, current slew rate $dI/dt = V/L$, and full-swing flux linkage $\Delta\Psi = 2LI_{max}$. RPM, angular velocity, and step angle come from standard rotational kinematics: $\omega = 2\pi \times \text{rev/s}$ and step angle $= 360^\circ / spr$.
The input mistake that causes the most confusion: many stepper motor datasheets list resistance and inductance “phase-to-phase” for two-phase bipolar motors — roughly double the per-phase values this formula needs. Entering the phase-to-phase inductance in place of $L$ overstates $L$ by about 2×, which halves the calculated maximum speed and understates what the motor can actually do.
Three errors that follow from this:
- Entering phase-to-phase resistance/inductance instead of the per-phase value the formula expects, which throws off every downstream output by roughly 2×.
- Using the motor’s nameplate voltage instead of the driver’s actual supply voltage — modern chopper drivers are routinely run well above nameplate voltage with current limiting doing the protection, and $V$ here means supply voltage.
- Reading “Maximum Motor Speed” as a hard ceiling. It’s the speed at which the winding just reaches rated current within one step period; the motor can be driven faster, but torque falls off above it because the current no longer reaches $I_{max}$ before the next step.
“Coil DC Resistance” in the results is not a measured winding spec — it’s $V/I_{max}$, the resistance implied by assuming the driver reaches rated current in steady state at the entered voltage. It won’t match a datasheet’s measured winding resistance if the driver is current-limiting below what that voltage would otherwise push through the coil.
Current Rise Across One Phase Winding, One Step
Common Questions About Stepper Motor Speed Limits
Why does raising the supply voltage increase maximum speed?
Current rise in an inductor follows $dI/dt = V/L$. A higher voltage forces the winding current up to $I_{max}$ faster, shrinking the minimum time needed per step and raising the step rate at which the motor still reaches full rated current.
Should I enter the motor’s rated voltage or the power supply voltage?
Enter the driver’s supply voltage. Stepper drivers are commonly run above the motor’s nameplate voltage, with the driver’s current limit — not the winding’s natural resistance — protecting the motor.
Is per-phase or phase-to-phase inductance correct here?
Per-phase. Datasheets that list phase-to-phase values (common for bipolar motors) show roughly double the per-phase inductance; using that figure directly will understate the calculated maximum speed by about 2×.
Can the motor run faster than the calculated maximum speed?
Yes, but torque drops off above it. The figure marks the step rate at which the winding current just reaches $I_{max}$ within one step period, not a hard mechanical limit.
Why doesn’t “Coil DC Resistance” match my motor’s datasheet?
It’s calculated as $V/I_{max}$ from your inputs, not measured from the winding. It only matches the datasheet’s resistance if the driver is a true constant-voltage (L/R) drive rather than a current-limiting chopper drive.